6mm Main Bonding on TN-S domestic install

[freedomrun]

TN-S, 60A Main Fuse, 16mm Tails, 16mm Earth.

Question - CU change required & at the moment has 6mm Main Earth Bonding to gas & Water, less than 0.05 Ohms continuity measured & good condition. I'm pretty sure that this 6mm size Main bonding is compliant - just thought i would check if i should be aware of any other issue with leaving this in place. Thanks.

 

[topquark]

think you'll find that BS7671 stipulates 10mm bonding for TNC-S.

Unless the line conductor or neutral conductor is 50mm or 70mm in which case it's 16mm or 25mm respectively.

Sorry, I could resist (must try harder!!!)

 

[telectrix]

is there any of that the pikeys ain't nicked?

 

[freedomrun]

50mm - 70mm on a domestic install - blimey - they must be using industrial ovens !!!!

 

[ezzzekiel]

After a lot of research on this matter it has been drawn to my attention (via ECA and ESC) that minimum 6mm main bonding can stay in place on existing instalations providing they show no signs of damage and are verified adequate, and is left at your discretion but should be noted on the eic.

refered to reg 132.2 (or there abouts dont have regs handy)
ADDITIONS AND ALTERATIONS.
no alterations to properties unless EXISTING bonding and earthing are verified as adequate for the alteration.

 

[oxocube]

and are verified adequate,

How do you do that?

 

[telectrix]

adiabatic.

 

[ezzzekiel]

how would you do it?

check no signs of thermal (or mechanical) damage do continuity test on conductor, check adiabatic Ze, Zs etc then make an informed decision.

this is not a get out of upgrading bonding clause and in my humble opinion it should be carried out when possible.

Also a mention that pme supply must be pre 1988 if existing bonding is to be left in situ to comply with electrical safety regs.

Looked into this as firm i worked for were replacing load of social housing consumer units but didnt want bonding replaced unless needed so wanted something a little more concrete than "my boss told me to do it"

 

[oxocube]

adiabatic.

Adiabatic is not applicable to bonding conductors.

Edit - A light came on and now I see what you're getting at.

 

[ezzzekiel]

im pretty sure tel knows this but there is a relationship between main earthing and bonding conductor sizing....

 

[telectrix]

Adiabatic is not applicable to bonding conductors.

and as ezzie says, use adiabatic to determine required size of main earth, then bonding needs to be not less than 50% of that. (TNC-S notwithstanding)

 

[topquark]

50mm - 70mm on a domestic install - blimey - they must be using industrial ovens !!!!

No one mentioned domestic, it was however was meant in jest as others were being somewhat pedantic about it

 

[freedomrun]

I actually mentioned DOMESTIC in my original post question as this is what the question was refering to.

On a Domestic TN-C-S with a 16mm bonding to the MET, my bonding to Gas and Water services must be 10mm if not mechanically protected?

 

[Octopus]

BS 7671 - 131.8 is worth a read

 

[just add water sparks]

show/hideQ12. When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?

Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded.

Regulation number(s)

• 132.16
• 544.1.1

Just had similar problem ,researched into threads.The above para taken from the Electricity Saftey Council. Question and Answers page , Alterations.Would appreciate any ones take on this ??? hope there is no stoney silence!!!!!! i take it this refers to the main bonding

 

[atkins_1]

was hoping to find some answers when i searched for this but all i found is a bunch of gits flirting with each other...!!!?!?!?!?!?:willy_nilly: